1. Field of the Invention
The present invention relates to an L-glutamic acid-producing microorganism and a method for producing L-glutamic acid using the microorganism. L-glutamic acid is widely used in the food industry, for example, as a raw material in the production of seasonings.
2. Brief Description of the Related Art
L-glutamic acid has been conventionally produced on an industrial scale by fermentation methods using coryneform bacteria which have L-glutamic acid-producing ability, such as bacteria belonging to the genus Brevibacterium or Corynebacterium. For this purpose, strains isolated from nature, or artificial mutants thereof, have been used.
Generally, wild-type strains of coryneform bacteria do not produce L-glutamic acid when excess biotin is present. Accordingly, L-glutamic acid production by coryneform bacteria is typically performed under biotin-limited conditions, or a surfactant or penicillin is added to the culture medium (Biosci. Biotech. Biochem., 1997, 61 (7), p 1109-1112). On the other hand, mutant strains that can produce L-glutamic acid in the presence of excess biotin are used for L-glutamic acid production. These strains include a surfactant-temperature-sensitive strain (WO99/02692), a penicillin-sensitive strain (JP-A-55-0124492), and a lysozyme-sensitive strain (WO00/14241). However, such mutant strains may often show a decrease in fatty acid or cell wall synthesis, and there has been some difficulty in producing L-glutamic acid using these strains while maintaining sufficient growth of the strains.
Meanwhile, a genetically modified strain in which a gene encoding α-ketoglutaric acid dehydrogenase (α-KGDH) is disrupted has been used to produce L-glutamic acid in the presence of excess biotin (WO95/34672). However, this α-KGDH gene-deficient strain grows slowly because the TCA cycle is blocked midway, and it is difficult to obtain a sufficient amount of cells required for L-glutamic acid production.
The yggB gene of coryneform bacteria is a homolog of the yggB gene of Escherichia coli (FEMS Microbiol Lett. 2003, 218 (2), p305-309, Mol Microbiol. 2004, 54 (2), p420-438), and has been reported to be a kind of mechanosensitive channel (EMBO J. 1999, 18 (7):1730-7). However, its effect on L-glutamic acid production has not been previously reported.